This application claims the priority of Japanese Patent Application No. 11-143519 filed on May 24, 1999, which is incorporated herein by reference.
The present invention relates to a probe microscope; and, in particular, to a probe microscope capable of attaining highly reliable sample information.
For example, for accurately grasping irregularities of a surface of a sample, a scanning tunneling microscope (STM) is used.
According to the principle of measurement in the STM, a probe made of a metal is caused to approach an electrically conductive sample to a distance of about 1 nm, and a minute voltage is applied therebetween, whereby a current flows. This current is known as tunneling current, and is sensitive to changes in the distance therebetween, such that it alters by substantially one digit at most with respect to a change of 0.1 nm.
Therefore, if the metal-made probe is attached to a precision actuator capable of three-dimensional driving, and the measurement sample surface is scanned so as to keep the tunneling current constant, then the distance therebetween will be held constant, and the probe will trace the irregularities of the sample surface on the atomic order.
Here, if the change in the voltage applied to the precision actuator is visualized, then it will correspond to the form of the sample surface.
Insulating samples which could not be observed by the STM can be observed by an atomic force microscope (AFM) derived from the STM.
The AFM detects, instead of the tunneling current used in the STM, the atomic force (attractive force or repulsive force) acting between the measurement sample surface and the probe.
Here, as the probe of the AFM, a metal-made cantilever probe 10 such as the one shown in FIGS. 1A and 1B is employed.
FIG. 1A is a front view thereof, whereas FIG. 1B is a top plan view thereof
If the cantilever probe 10 is caused to approach the measurement sample surface 12 while being minutely vibrated up down (in the directions of Vv) in FIG. 1A, then an atomic force will act therebetween, thereby changing the amplitude of vibration of the probe 10.
Hence, probe light L1 from a probe irradiating portion 14 irradiates the probe 10, and the change in intensity of transmitted or reflected probe light L2 from the probe 10 is detected by a photodetector 16. From this change in intensity, information about the change in amplitude of vibration of the probe 10 is obtained.
If the distance therebetween is determined from the change in amplitude of vibration, and the stage mounting the measurement sample is driven to scan the measurement sample surface such that the change in amplitude of vibration is kept constant while the probe position is fixed, then the distance therebetween will be held constant, and the probe can accurately trace the irregularities of the measurement sample surface.
If the metal-made cantilever probe 10 is vibrated up and down (in the directions of Vv) in FIG. 1A, on the other hand, then ingredients of the sample at the probe position and the like cannot be analyzed while the irregularities of the measurement sample surface 12 can be grasped accurately.
Therefore, in recent years, near-field optical microscopes, having a spatial resolution smaller than the wavelength of light, capable of spectral analysis and measurement, have been developed with expectation for their applications.
The near-field optical microscopes include two systems, i.e., collection mode in which an optical near-field occurring in the measurement sample surface is scattered at a needle-like probe tip portion and collected so as to be detected, and illumination mode in which the measurement sample surface is illuminated with the near-field light occurring from the needle-like probe tip portion and the light scattered or released by the measurement sample surface is collected and detected by the probe or a light-collecting optical system.
In any case, the optical near field is generated in an area on the order of several tens of nanometers from the measurement sample surface, whereby the distance between the measurement sample surface and the fiber probe must be controlled within a very minute distance not longer than the wavelength of light.
For controlling the distance between the measurement sample surface and the probe, shear force feedback method is employed in general.
In the shear force feedback method, as shown in FIGS. 2A and 2B, a needle-like probe 18 is caused to approach the measurement sample surface 12 while being uniaxially vibrated (in the directions of VH) on the measurement sample surface 12.
FIG. 2A is a front view thereof, whereas FIG. 2B is a top plan view thereof When the distance between the measurement sample surface 12 and the probe 18 falls within the reach of the optical near field, then a shear force acts therebetween, thereby changing the amplitude of vibration of the probe 18.
Hence, probe light L1 from the probe irradiating portion 14 irradiates the fiber probe 18, and the change in intensity of transmitted or reflected probe light L2 from the probe 10 is detected by the photodetector 16. From this change in intensity, information about the change in amplitude of vibration of the probe 18 is obtained.
If the distance therebetween is determined from the change in amplitude of vibration, and the stage mounting the measurement sample is driven to scan the measurement sample surface such that the change in amplitude of vibration of the needle-like probe 18 is kept constant while the probe position is fixed, then the distance therebetween will be held constant, and the needle-like probe 18 can accurately trace the irregularities of the measurement sample surface on the atomic order.
Thus, when the needle-like probe 18 is used for carrying out the illumination mode or collection mode, not only the irregularities of the measurement sample surface 12 can be grasped, but also ingredients of the sample at the probe position and the like can be analyzed.
However, such a needle-like probe 18 is also uniaxially vibrated on the measurement sample surface, and the lateral shift component of the atomic force acting between the measurement sample surface and the probe is detected, whereby its sensitivity would lower by one digit or more when compared with the case where the vertical component of the atomic force is measured with the cantilever probe 10.
If a shear force uniaxially vibrating the probe on the measurement sample surface is employed, then there may be a fear of a difference occurring in the obtained image of irregularities of measurement sample surface, depending on the scanning direction of the measurement sample surface, even in the same measurement sample surface.
Hence, the reliability of measurement results with the needle-like probe 18 has still a room for improvement, but no techniques for achieving it have been known yet.
In view of the above-mentioned background art, it is an object of the present invention to provide a probe microscope capable of attaining sample information with a higher reliability.
For achieving the above-mentioned object, the probe microscope in accordance with the present invention is a probe microscope for causing a measurement sample surface and a tip portion of a probe on the sample side to approach each other, detecting an interaction between the measurement sample surface and the tip portion of the probe on the sample side, and obtaining surface information of the measurement sample from the interaction; the probe microscope comprising vibrating means and detecting means.
Here, the probe is a flexible needle-like probe.
The vibrating means is capable of rotating the probe while flexing the tip portion thereof on the sample side so as to draw a circle having a size corresponding to an increase and decrease in the interaction between the measurement sample surface and the tip portion of the probe on the sample side.
The detecting means detects the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side due to the interaction between the measurement sample surface and the tip portion of the probe on the sample side and obtains, from the increase and decrease in the size of the circle, information about the distance between the measurement sample surface and the tip portion of the probe on the sample side.
Here, the circle encompasses not only true circles but also ellipses and the like.
Preferably, in the present invention, while the vibrating means also vibrates the probe in a direction in which the measurement sample surface and the tip portion of the probe on the sample side approach each other or move away from each other, the detecting means detects the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side due to the interaction between the measurement sample surface and the tip portion of the probe on the sample side and obtains, from the increase and decrease in the size of the circle, information about the distance between the measurement sample surface and the tip portion of the probe on the sample side.
Preferably, in the present invention, the vibrating means includes one driving member selected from the group consisting of a piezoelectric element and a motor which are capable of rotating the probe while flexing the tip portion thereof on the sample side such that at least the tip portion of the probe on the sample side draws a circle having a size corresponding to an increase and decrease in the interaction between the measurement sample surface and the tip portion of the probe on the sample side.
Preferably, in the present invention, the detecting means comprises a probe irradiating portion, a photodetector portion, and a signal processing portion.
Here, the probe irradiating portion is capable of irradiating the probe with probe light.
The photodetector portion detects reflected or transmitted probe light from the probe.
The signal processing portion obtains, from the reflected or transmitted probe light obtained by the photodetector portion, information about the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side.
Preferably, in the present invention, the detecting means is one member selected from the group consisting of a quartz vibrator and a piezoelectric element which are capable of obtaining information about the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side.
Preferably, the probe microscope in accordance with the present invention comprises a divided type piezoelectric element divided into four or more, for example, having a vibrating electrode pair placed face to face as the vibrating means and a detecting electrode pair placed face to face as the detecting means, which are arranged alternately over substantially the whole periphery on the opposite side of the probe from the tip portion on the sample side; and control means for causing the vibrating electrode pair to vibrate the probe and the detecting electrode pair to detect the increase and decrease in the size of the circle simultaneously or alternately in a time series.
Preferably, in the present invention, the interaction between the measurement sample surface and the tip portion of the probe on the sample side is a dynamic interaction such as an atomic force.
Preferably, in the present invention, the interaction between the measurement sample surface and the tip portion of the probe on the sample side is an optical near field.
Preferably, the probe microscope in accordance with the present invention further comprises scanning means and visualizing means.
Here, the scanning means is capable of scanning the measurement sample surface such that the distance between the measurement sample surface and the tip portion of the probe on the sample side obtained by the detecting means is kept constant.
The visualizing means visualizes control information of the scanning means, so as to visualize information about irregularities in the measurement sample surface.
Thus, the probe microscope in accordance with the present invention is configured such that the probe is a flexible needle-like probe such as a fiber probe, for example; the vibrating means rotates the probe while flexing the tip portion thereof on the sample side so as to draw a circle having a size corresponding to an increase and decrease in the interaction between the measurement sample surface and the tip portion of the probe on the sample side; and the detecting means detects the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side due to the interaction between the measurement sample surface and the tip portion of the probe on the sample side and obtains, from the increase and decrease in the size of the circle, information about the distance between the measurement sample surface and the tip portion of the probe on the sample side.
As a result, in the present invention, the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side due to the interaction between it and the measurement sample surface is detected, so as to detect the interaction of the longitudinal component, whereby the sensitivity of detection improves as compared with cases where typical lateral shift components such as shear force are detected.
Also, since the flexible needle-like probe such as fiber probe, for example, is employed, the present invention makes it possible to simultaneously analyze ingredients of the sample at the probe position and the like, which has been quite difficult with a typical metal-made cantilever probe.
Since the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side due to the interaction between the probe and the measurement sample surface is detected, and information about the distance between the measurement sample surface and the probe is obtained from the increase and decrease in the size of the circle, there are no restrictions concerning the arrangement and number of detecting means and the like.
As a consequence, in the present invention, a freedom in arrangement of individual constituents of the detecting means, which has conventionally been quite hard to obtain, can be attained, and detection with a higher sensitivity can be carried out if the number of detecting means is increased, since the resulting amount of distance information such as the intensity of reflected or transmitted probe light will enhance thereby.
Since the increase and decrease in the size of the circle drawn by the tip portion of the probe on the sample side due to the interaction between the probe and the measurement sample surface is detected, the probe microscope of the present invention can carry out isotropic measurement, independent of the scanning direction of the measurement sample surface, which has been quite difficult in cases where typical lateral shift components such as shear force are detected or where a vertically vibrating cantilever probe is simply employed.
When the present invention uses one driving member selected from the group consisting of a piezoelectric element and a motor which are capable of rotating the probe while flexing the tip portion thereof on the sample side such that at least the tip portion of the probe on the sample side draws a circle having a size corresponding to an increase and decrease in the interaction between the measurement sample surface and the tip portion of the probe on the sample side, the probe can be vibrated favorably in a simple configuration.
When the present invention comprises a divided type piezoelectric element divided into four or more, for example, having a vibrating electrode pair placed face to face as the vibrating means and a detecting electrode pair placed face to face as the detecting means, which are arranged alternately over substantially the whole periphery on the opposite side of the probe from the tip portion on the sample side, and control means for causing the vibrating electrode pair to vibrate the probe and the detecting electrode pair to detect the increase and decrease in the size of the circle simultaneously or alternately in a time series, then space can be saved more as compared with the case where the vibrating means and the detecting means are provided independently from each other. As a consequence, the apparatus can be made smaller.
When scanning means scans the measurement sample such that the distance between the measurement sample surface and the tip portion of the probe on the sample side obtained by the detecting means is kept constant, and the visualizing means visualizes control information of the scanning means, so as to visualize information about irregularities in the measurement sample surface, then the information about irregularities in the measurement sample surface can be grasped accurately in the present invention.